The invention pertains to the art of manufacture of cylindrical sleeves and more particularly to cylindrical sleeves having grooves or slots.
The invention is particularly applicable to the manufacture of a rotary valve sleeve employed in an automotive power steering gear assembly wherein a plurality of spaced grooves on the inner cylindrical walls of the valve sleeve need be closed at their terminal ends to contain and control fluid flow for the steering assembly. However, it will be appreciated to those skilled in the art that the invention could be readily adapted for use in other environments as, for example, where grooves spaced in an item wall need be closed at their terminal ends with a minimum of applied force and resulting distortion to the item.
Rotary valve sleeves are common components of power assist assemblies and are particularly common in automotive power steering assemblies to control the flow of fluid in accordance with the desired operation of the gear and valve. The rotary valve sleeve is typically of a generally cylindrical configuration including a plurality of circumferential grooves along the outer wall of the sleeve, and a plurality of spaced axial grooves along the inner sleeve wall for the conduct and communication of fluid through various flow paths. Radial bore holes communicate several of the outer wall grooves with several associated inner wall grooves. A typical rotary valve sleeve and prior art method of manufacturing same is shown in U.S. Pat. No. 4,419,877.
A feature of the manufacture of such valve sleeves involves substantially closing the terminal end portions of the inner wall grooves relative to the inner wall to contain fluid within the groove between the sleeve and the shaft received within the sleeve. Various methods of manufacture have been suggested to effect closing of the grooves. It has been found that the defects present in such methods are such that the methods themselves and the resulting work pieces have limited economic and practical value.
One particularly common method of manufacture of a rotary valve sleeve includes positioning an annular ring in the sleeve adjacent the terminal end portions of the inner wall grooves. The ring has an inner diameter substantially equal to the inner wall so that the grooves are substantially closed off. The ring may be fixed to this position in any of a variety of known ways.
The particular disadvantage of this method is cost. The cost to supply two additional annular ring components requiring close tolerance specifications has been particularly undesirable.
In addition, there are the obvious problems associated with the assembly and maintenance of a multi-component device.
An alternative method of manufacture includes orbital forming of an annular bead at a shoulder on the sleeve adjacent the groove terminal end portions. Orbital forming comprises moving or rolling a tool around the shoulder part under a lot of pressure in an orbital fashion. The rolling single point contact would deform the shoulder as the tool moved to form an annular bead disposed toward the sleeve inner wall. This method of manufacture failed for the particular problem of producing work parts that would crack and break and which were accordingly totally unsafe. It was suggested to first heat the part before the orbital forming operation which did provide some improvement, but even so, the problems of sleeve cracking and breaking remained.
It is also known to close the terminal end portions of the inner grooves with straight crushing or swedging by abutting a punch against the complete circumference of the inner wall shoulders adjacent the groove terminal ends to deform the shoulders and produce a bead for closing the groove end. Such punches have comprised annularly configured devices to produce a continuous annular bead about the shoulder. Usually the method involves simultaneous straight abutment against opposite shoulders at the opposite ends of the inner grooves for simultaneous deformation and production of the continuous annular bead at each end of the internal grooves.
It has been found that the defects present in such a method of manufacture of a rotary valve sleeve are such that the method and resulting work pieces have limited economic and practical value.
However, the necessity for maintaining close size and configuration specifications of the rotary valve work piece during manufacture has increased over time in accordance with increased demand for quality control. The component work pieces themselves as well as their assembly in the straight swedging technique have been unable to perform in accordance with demand. Such demand now dictates that the size and configuration specifications of an item such as a rotary valve sleeve be maintained within thousandths of an inch during manufacture to be acceptable in the marketplace. Such close tolerances have placed a burden upon manufacturers to improve methods of manufacture to maintain such standards.
The straight swedging method of manufacturing a rotary valve sleeve has been unable to maintain the desired tolerances due to the resulting distortion to the work pieces.
More particularly, the forces necessary to punch an annular bead on a conventional rotary valve sleeve for closing inner wall grooves at their terminal ends are in the nature of 20 tons. When such a force is applied to a typical work piece which is less than two inches long and an inch and one half in diameter, it is obvious that distortion will occur to not only the overall length of the sleeve, but to numerous other parts and sections of the sleeve such as circumferential grooves along the outer wall and the compression of radial bores extending through the sleeve side wall.
Another problem with conventional methods is the consumption of large amounts of energy. For example, the expense to apply a force in the order of 20 tons adds to the cost of the manufacture of the valve sleeve itself. Also, such large forces are expected to present dangers and risks to workers involved in the manufacture and exposed to the operation and application of the necessary punching equipment.
The present invention contemplates a new and improved method of manufacture of a valve sleeve which overcomes all of the above referenced problems and others to provide a new method of manufacture which is simple in design, economically more efficient in manufacture, readily adaptable to a plurality of valve sleeves having a variety of dimensional characteristics, easy to operate and which provides improved sleeve work pieces having improved size and configuration specifications and tolerances.